void AddDoc(IndexWriter writer, string lang, string source, string group, string text)
{
Field f0 = new Field("lang", lang, Field.Store.YES, Field.Index.NOT_ANALYZED);
Field f1 = new Field("source", source, Field.Store.YES, Field.Index.NOT_ANALYZED);
Field f2 = new Field("category", group, Field.Store.YES, Field.Index.NOT_ANALYZED);
Field f3 = new Field("text", text, Field.Store.YES, Field.Index.ANALYZED);
Document doc = new Document();
doc.Add(f0);
doc.Add(f1);
doc.Add(f2);
doc.Add(f3);
writer.AddDocument(doc);
}